Development of spontaneous stereotyped behavior in deer mice: Effects of early and late exposure to a more complex environment

Abnormal repetitive behaviors such as stereotypies are associated with neur odevelopmental disorders and are often observed under conditions of environ mental restriction, particularly early in development. Few studies, however , have systematically assessed the effects of environmental enrichment and almost no information is available as to Ir whether a sensitive period exis ts for such enrichment effects. We hypothesized that spontaneous stereotypi es exhibited by deer mice housed under standard laboratory conditions were the result of environmental restriction and that a sensitive period exists for the development/prevention of stereotypies. Exposure to a more complex environment early in the post-weaning period resulted in substantially less stereotypy the complex environment. importantly, this outcome was maintain ed even after mice,were housed in standard cages for an identical period of time. Later exposure to the more complex environment also resulted in sign ificantly lower levels of stereotypy compared to controls. These effects rr ere observed in the experimental housing condition as well as in a standar d test context. The effects of early and late enrichment support the import ance of environmental restriction in the genesis of stereotypy and provide support for the efficacy of early and late enrichment in the prevention of stereotypies. (C) 2000 John Wiley & Sons, Inc.